This invention relates to a method for adjusting the calibration of a circuit breaker trip mechanism. More particularly, this invention relates to a method for thermally calibrating a bimetal trip mechanism of a circuit breaker. This invention also relates to a circuit breaker trip mechanism produced by the method.
Circuit breakers have movable contact elements and operating mechanisms for protecting an electrical circuit from such undesirable conditions as current overload and short circuiting. Generally, a trip mechanism having a bimetal element is provided for controlling the position of a toggle switch and concomitantly the engagement of the movable contact elements. The bimetal element is part of a trip structure which moves relative to a trip bar in dependence on the amount of current flow. Higher current differentially increases temperature in the bimetal element and causes a displacement towards the trip bar. Sufficiently high current causes trip bar actuation and circuit breaking. A set screw is typically provided in the trip structure to adjust the rest position of the bimetal element relative to the trip bar. However, the trip distance is sometimes improperly set owing to variations in the manufacturing process.